High velocity compression damping valve

ABSTRACT

A shock absorber includes a pressure sensitive valve assembly that controls fluid flow through the pressure sensitive valve assembly based upon the velocity of the piston assembly in the shock absorber. The pressure sensitive valve assembly restricts fluid flow as the velocity of the piston in a compression stroke increases to increase the damping loads provided by the shock absorber. A secondary valve assembly controls fluid flow through the pressure sensitive valve assembly when the pressure sensitive valve assembly is in a closed position.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 12/496,964 filed on Jul. 2, 2009 which claims the benefit ofProvisional U.S. Patent Application No. 61/100,321 filed Sep. 26, 2008.The entire disclosures of which are incorporated herein by reference.

FIELD

The present disclosure relates generally to shock absorbers or dampers.More particularly, the present disclosure relates to a shock absorber ordamper having a base valve assembly which includes a pressure sensitivevalve assembly for high speed damping.

BACKGROUND

This section provides background information related to the presentdisclosure which is not necessarily prior art.

Shock absorbers are used in conjunction with automotive suspensionsystems and other suspension systems to absorb unwanted vibrations whichoccur during movement of the suspension system. In order to absorb theseunwanted vibrations, automotive shock absorbers are generally connectedbetween the sprung (body) and the unsprung (suspension/chassis) massesof the automobile.

The most common type of shock absorbers for automobiles are the dashpottype in which a piston is located within a pressure tube and isconnected to the sprung mass of the vehicle through a piston rod. Thepiston divides the pressure tube into an upper working chamber and alower working chamber. Because the piston, through valving, has theability to limit the flow of damping fluid between the upper and lowerworking chambers within the pressure tube when the shock absorber iscompressed or extended, the shock absorber is able to produce a dampingforce which counteracts the vibrations which would otherwise betransmitted from the unsprung mass to the sprung mass. In a dual tubeshock absorber, a fluid reservoir is defined between the pressure tubeand a reserve tube which is positioned around the pressure tube. A basevalve is located between the lower working chamber and the fluidreservoir to also produce a damping force which counteracts thevibration which would otherwise be transmitted from the unsprung portionto the sprung portion of the automobile during stroking of the shockabsorber.

Some applications or suspension systems that are developed could benefitby utilizing a displacement sensitive damping concept, a velocitysensitive damping concept and/or an acceleration sensitive concept.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

The present disclosure provides a shock absorber or damper whichincorporates high speed damping by using a base valve assembly whichincreases the amount of damping load generated as the velocity of thepiston increases during a compression stroke of the shock absorber ordamper. A pressure responsive device is incorporated into the base valveassembly to increase the damping load in response to an increase inpressure of the working chamber caused by the increase in velocity ofthe piston in the pressure tube during a compression stroke.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 is a schematic representation of a typical automobile whichincorporates the high velocity compression damping valve in accordancewith the present disclosure;

FIG. 2 is a side sectional view of a shock absorber which incorporatesthe high velocity compression damping in accordance with the presentdisclosure;

FIG. 3 is an enlarged cross-sectional view of the piston assemblyillustrated in FIG. 2;

FIG. 4 is an enlarged cross-sectional view of the base valve assemblyillustrated in FIG. 2 in an open position;

FIG. 5 is an enlarged cross-sectional view of the base valve assemblyillustrated in FIG. 4 in a closed position;

FIG. 6 is an enlarged cross-sectional view of a base valve assembly inaccordance with another embodiment of the present disclosure in an openposition;

FIG. 7 is an enlarged cross-sectional view of a base valve assembly inaccordance with another embodiment of the present disclosure in an openposition;

FIG. 8 is an enlarged cross-sectional view of a base valve assembly inaccordance with another embodiment of the present disclosure in an openposition;

FIG. 9 is an enlarged cross-sectional view of a base valve assembly inaccordance with another embodiment of the present disclosure in an openposition;

FIG. 10 is an enlarged cross-sectional view of a base valve assembly inaccordance with another embodiment of the present disclosure in an openposition;

FIG. 11 is a side cross-sectional view of a monotube shock absorberwhich incorporates the high velocity compression damping in accordancewith the present disclosure;

FIG. 12 is an enlarged cross-sectional view of a base valve assembly inaccordance with another embodiment of the present disclosure in an openposition; and

FIG. 13 is an enlarged cross-sectional view of the base valve assemblyillustrated in FIG. 12 in a closed position.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference tothe accompanying drawings.

The following description of the preferred embodiment(s) is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses.

Referring now to the drawings in which like reference numerals designatelike or corresponding parts throughout the several views; there is shownin FIG. 1 a vehicle incorporating a suspension system incorporating theshock absorbers in accordance with the present invention and which isdesignated generally by the reference numeral 10. Vehicle 10 includes arear suspension 12, a front suspension 14 and a body 16. Rear suspension12 has a transversely extending rear axle assembly (not shown) adaptedto operatively support a pair of rear wheels 18 of vehicle 10. The rearaxle assembly is operatively connected to body 16 by means of a pair ofshock absorbers 20 and a pair of helical coil springs 22. Similarly,front suspension 14 includes a transversely extending front axleassembly (not shown) to operatively support a pair of front wheels 24 ofvehicle 10. The front axle assembly is operatively connected to body 16by means of a second pair of shock absorbers 26 and by a pair of helicalcoil springs 28. Shock absorbers 20 and 26 serve to dampen the relativemotion of the unsprung mass (i.e., front and rear suspensions 12 and 14,respectively) and the sprung mass (i.e., body 16) of vehicle 10. Whilevehicle 10 has been depicted as a passenger car having front and rearaxle assemblies, shock absorbers 20 and 26 may be used with other typesof vehicles or in other types of applications such as vehiclesincorporating independent front and/or independent rear suspensionsystems. Further, the term “shock absorber” as used herein is meant torefer to dampers in general and thus will include MacPherson struts.

Referring now to FIG. 2, shock absorber 20 is shown in greater detail.While FIG. 2 illustrates only shock absorber 20, it is to be understoodthat shock absorber 26 also includes the base valve assembly describedbelow for shock absorber 20. Shock absorber 26 only differs from shockabsorber 20 in the manner in which it is adapted to be connected to thesprung and unsprung masses of vehicle 10. Shock absorber 20 comprises apressure tube 30, a piston assembly 32, a piston rod 34, a reserve tube36 and a base valve assembly 38.

Pressure tube 30 defines a working chamber 42. Piston assembly 32 isslidably disposed within pressure tube 30 and divides working chamber 42into an upper working chamber 44 and a lower working chamber 46. A seal48 is disposed between piston assembly 32 and pressure tube 30 to permitsliding movement of piston assembly 32 with respect to pressure tube 30without generating undue frictional forces as well as sealing upperworking chamber 44 from lower working chamber 46. Piston rod 34 isattached to piston assembly 32 and extends through upper working chamber44 and through end cap 50 which closes the upper end of pressure tube30. A sealing system seals the interface between upper end cap 50,reserve tube 36 and piston rod 34. The end of piston rod 34 opposite topiston assembly 32 is adapted to be secured to the sprung portion ofvehicle 10. Valving within piston assembly 32 controls the movement offluid between upper working chamber 44 and lower working chamber 46during movement of piston assembly 32 within pressure tube 30. Becausepiston rod 34 extends only through upper working chamber 44 and notlower working chamber 46, movement of piston assembly 32 with respect topressure tube 30 causes a difference in the amount of fluid displaced inupper working chamber 44 and the amount of fluid displaced in lowerworking chamber 46. The difference in the amount of fluid displaced isknown as the “rod volume” and it flows through base valve assembly 38.

Reserve tube 36 surrounds pressure tube 30 to define a fluid reservoirchamber 52 located between tubes 30 and 36. The bottom end of reservetube 36 is closed by an end cap 54 which is adapted to be connected tothe unsprung portion of vehicle 10. While end cap 54 is illustrated as aseparate component, it is within the scope of the present disclosure tohave end cap 54 integral with reserve tube 36. The upper end of reservetube 36 is attached to upper end cap 50. Base valve assembly 38 isdisposed between lower working chamber 46 and reservoir chamber 52 tocontrol the flow of fluid between chambers 46 and 52. When shockabsorber 20 extends in length, an additional volume of fluid is neededin lower working chamber 46 due to the “rod volume” concept. Thus, fluidwill flow from reservoir chamber 52 to lower working chamber 46 throughbase valve assembly 38 as detailed below. When shock absorber 20compresses in length, an excess of fluid must be removed from lowerworking chamber 46 due to the “rod volume” concept. Thus, fluid willflow from lower working chamber 46 to reservoir chamber 52 through basevalve assembly 38 as detailed below.

Referring now to FIG. 3, piston assembly 32 comprises a piston body 60,a compression valve assembly 62 and a rebound valve assembly 64.Compression valve assembly 62 is assembled against a shoulder 66 onpiston rod 34. Piston body 60 is assembled against compression valveassembly 62 and rebound valve assembly 64 is assembled against pistonbody 60. A nut 68 secures these components to piston rod 34.

Piston body 60 defines a plurality of compression passages 70 and aplurality of rebound passages 72. Seal 48 includes a plurality of ribs74 which mate with a plurality of annular grooves 76 to restrict slidingmovement of seal 48 relative to piston body 60 as piston assembly 32slides in pressure tube 30.

Compression valve assembly 62 comprises a retainer 78, a valve disc 80and a spring 82. Retainer 78 abuts shoulder 66 on one end and pistonbody 60 on the other end. Valve disc 80 abuts piston body 60 and closescompression passages 70 while leaving rebound passages 72 open. Spring82 is disposed between retainer 78 and valve disc 80 to bias valve disc80 against piston body 60. During a compression stroke, fluid in lowerworking chamber 46 is pressurized causing fluid pressure to reactagainst valve disc 80. When the fluid pressure against valve disc 80overcomes the biasing load of spring 82, valve disc 80 separates frompiston body 60 to open compression passages 70 and allow fluid flow fromlower working chamber to upper working chamber. Typically spring 82 onlyexerts a light load on valve disc 80 and compression valve assembly 62acts like a check valve between chambers 46 and 44. The dampingcharacteristics for shock absorber 20 during a compression stroke ofshock absorber 20 are controlled by base valve assembly 38 whichaccommodates the flow of fluid from lower working chamber 46 toreservoir chamber 52 due to the “rod volume” concept as detailed below.During a rebound stroke, compression passages 70 are closed by valvedisc 80.

Rebound valve assembly 64 comprises a spacer 84, a plurality of valvediscs 86, a retainer 88 and a spring 90. Spacer 84 is threadinglyreceived on piston rod 34 and is disposed between piston body 60 and nut68. Spacer 84 retains piston body 60 and compression valve assembly 62while permitting the tightening of nut 68 without compressing eithervalve disc 80 or valve discs 86. Retainer 78, piston body 60 and spacer84 provide a continuous solid connection between shoulder 66 and nut 68to facilitate the tightening and securing of nut 68 to spacer 84 andthus to piston rod 34. Valve discs 86 are slidingly received on spacer84 and abut piston body 60 to close rebound passages 72 while leavingcompression passages 70 open. Retainer 88 is also slidingly received onspacer 84 and it abuts valve discs 86. Spring 90 is assembled overspacer 84 and is disposed between retainer 88 and nut 68 which isthreadingly received on spacer 84. Spring 90 biases retainer 88 againstvalve discs 86 and valve discs 86 against piston body 60. The pluralityof valve discs 86 comprise a bleed disc 92, a valve disc 94, a spacerdisc 96 and a fulcrum disc 98. Bleed disc 92 includes at least one slot100 which permits a limited amount of bleed flow bypassing rebound valveassembly 64. Fulcrum disc 98 provides a fulcrum or bending point forbleed disc 92, valve disc 94 and spacer disc 96. When fluid pressure isapplied to discs 92 and 94, they will elastically deflect at the outerperipheral edge of spacer disc 96 and fulcrum disc 98 to open reboundvalve assembly 64. A shim 102 is located between nut 68 and spring 90 tocontrol the preload for spring 90 and thus the blow off pressure asdescribed below. Thus, the calibration for the blow off feature ofrebound valve assembly 64 is separate from the calibration forcompression valve assembly 62.

During a rebound stroke, fluid in upper working chamber 44 ispressurized causing fluid pressure to react against valve discs 86. Whenthe fluid pressure reacting against valve discs 86 overcomes the bendingload for valve discs 86, valve discs 86 elastically deflect openingrebound passages 72 allowing fluid flow from upper working chamber 44 tolower working chamber 46. The strength of valve discs 86 and the size ofrebound passages will determine the damping characteristics for shockabsorber 20 in rebound. Prior to the deflection of valve discs 86, acontrolled amount of fluid flows from upper working chamber 44 to lowerworking chamber 46 through slot 100 to provide low speed tunability.When the fluid pressure within upper working chamber 44 reaches apredetermined level, the fluid pressure will overcome the biasing loadof spring 90 causing axial movement of retainer 88 and the plurality ofvalve discs 86. The axial movement of retainer 88 and valve discs 86fully opens rebound passages 72 thus allowing the passage of asignificant amount of damping fluid creating a blowing off of the fluidpressure which is required to prevent damage to shock absorber 20 and/orvehicle 10. Additional fluid required to be added to lower workingchamber 46 due to the “rod volume” concept will flow through base valveassembly 38.

Referring now to FIGS. 4 and 5, base valve assembly 38 is illustrated.Base valve assembly 38 comprises a cylinder end 110, a rebound valveassembly 112, a compression valve assembly 114 and a pressure sensitivevalve assembly 116. Cylinder end 110 is attached to pressure tube 30 andseparates lower working chamber 46 from reservoir chamber 52. Cylinderend 110 engages end cap 54 and it defines a plurality of fluid passages122 open to reservoir chamber 52. Cylinder end 110 defines a centralpassage 124 extending between lower working chamber 46 and reservoirchamber 52 through fluid passages 122, a plurality of rebound fluidpassages 126 extending between lower working chamber 46 and reservoirchamber 52 through fluid passages 122 and a plurality of compressionfluid passages 128 extending between lower working chamber 46 andreservoir chamber 52 through fluid passages 122.

Rebound valve assembly 112 comprises one or more valve discs 130 and avalve spring 132. Valve discs 130 close the plurality of rebound fluidpassages 126 and valve spring 132 is disposed between pressure sensitivevalve assembly 116 and valve disc 130 to bias valve disc 130 againstcylinder end 110. During a rebound stroke of shock absorber 20, the “rodvolume” concept requires fluid to flow from reservoir chamber 52 tolower working chamber 46. The rebound stroke reduces the fluid pressurewithin lower working chamber 46 and the fluid pressure within reservoirchamber 52 will exceed the fluid pressure within lower working chamber46. The fluid pressure within reservoir chamber 52 will react againstvalve disc 130 and when the load on valve disc 130 from the fluidpressure exceeds the biasing load of valve spring 132, valve disc 130will unseat from cylinder end 110 and fluid will flow from reservoirchamber 52 through fluid passages 122, through rebound fluid passages126 and into lower working chamber 46. Valve spring 132 is designed toexert a minimum load against valve disc 130 such that rebound valveassembly 112 acts like a check valve during a rebound stroke and doesnot substantially contribute to the damping loads for shock absorber 20.The damping load during a rebound stroke for shock absorber 20 iscreated by rebound valve assembly 64 of piston assembly 32.

Compression valve assembly 114 comprises one or more valve discs 140 anda bolt 142. Valve discs 140 close the plurality of compression fluidpassages 128 and bolt 142 threadingly engages pressure sensitive valveassembly 116 to secure valve disc 140 against cylinder end 110. During acompression stroke of shock absorber 20, the “rod volume” conceptrequires fluid to flow from lower working chamber 46 to reservoirchamber 52. During the compression stroke, fluid pressure in lowerworking chamber 46 increases and this fluid pressure reacts againstvalve discs 140. As the fluid pressure within lower working chamber 46increases, the fluid pressure reacts against valve discs 140 andeventually valve discs 140 will deflect to open compression fluidpassages 128. Fluid will flow from lower working chamber 46, throughcompression fluid passages 128, through fluid passages 122 and intoreservoir chamber 52. The damping load during a compression stroke iscreated by compression valve assembly 114. As described above,compression valve assembly 62 of piston assembly 32 acts like a checkvalve and does not substantially contribute to the damping loads forshock absorber 20. Compression valve assembly 114 is a normally closedcompression valve assembly which is opened by the pressure differentialbetween lower working chamber 46 and reservoir chamber 52. The flowthrough compression valve assembly 114 is directly proportional to thepressure differential. The greater the pressure differential, thegreater deflection of valve discs 140 and the greater the flow throughcompression valve assembly 114.

Pressure sensitive valve assembly 116 is a pressure actuated valveassembly which comprises cylinder end 110, a stem 150, a spool 152, aspool cap 154 and a valve spring 156. Stem 150 is disposed withincentral passage 124 and is secured to cylinder end 110 by bolt 142 ofcompression valve assembly 114. Bolt 142 defines a central fluid passage158 and stem 150 defines a central fluid passage 160 to provide for apressure drop as described below.

Spool 152 is slidingly received over stem 150. Upward movement of spool152 on stem 150 is limited by a flange 162 on stem 150 which engages ashoulder 164 defined by spool 152. Valve spring 132 of rebound valveassembly 112 and valve spring 156 of pressure sensitive valve assembly116 biases shoulder 164 of spool 152 against flange 162 of stem 150 toallow fluid to flow from lower working chamber 46 into the plurality ofcompression fluid passages 128. Spool cap 154 is secured to spool 152.Spool 152 defines one or more holes 166.

During a compression stroke, fluid pressure within lower working chamber46 acts against spool 152 and spool cap 154 of pressure sensitive valveassembly 116. The fluid pressure within reservoir chamber 52 actsagainst spool 152 and spool cap 154 of pressure sensitive valve assembly116. The reservoir fluid pressure is channeled to spool 152 and spoolcap 154 through fluid passages 122, 158 and 160. The biasing of valvespring 132 and valve spring 156 allows for the normal flow of fluidthrough compression valve assembly 114 as described above as long as thepressure difference across spool 152 does not generate sufficient loadto overcome the biasing load of valve spring 132 and valve spring 156.Once the pressure differential acting on spool 152 exceeds the biasingload of valve spring 132 and valve spring 156, spool 152 will slidedownward on stem 150 and close or prohibit fluid flow from lower workingchamber 46 to the plurality of compression fluid passages 128 asillustrated in FIG. 5. Once the fluid pressure across spool 152 reduces,valve spring 132 and valve spring 156 will again bias spool 152 upwardagainst flange 162. When spool 152 closes or prohibits fluid flow, thefluid pressure in lower working chamber 46 exponentially increases andthe only flow between lower working chamber 46 and reservoir chamber 58is through the one or more holes 166 and compression valve assembly 114.The area of the one or more holes 166 and the instantaneous velocity ofpiston assembly 32 will define the final damping forces achieved. Theincrease in fluid pressure within lower working chamber 46 is a functionof the velocity of piston assembly 32 and thus pressure sensitive valveassembly 116 is a pressure sensitive valve which opens and closes basedupon the velocity of piston assembly 32. Pressure sensitive valveassembly 116 is a normally open compression valve assembly which isclosed by the pressure differential between lower working chamber 46 andreservoir chamber 52 where the pressure differential is determined bythe velocity of piston assembly 32.

The movement of spool 152 can be controlled or damped by controlling thediameter of central fluid passage 158 of bolt 142. As illustrated inFIG. 4, a fluid chamber 170 is located above bolt 142. This volume mustbe displaced through central fluid passage 158 in order for spool 152 tomove downward. By controlling the diameter of central fluid passage 158the period of time that it takes spool 152 to move downward can becontrolled. Thus, a damping effect can be achieved in regard to thismotion of spool 152.

Pressure sensitive valve assembly 116 can also be converted to anacceleration sensitive valve assembly. By eliminating central fluidpassage 158 and eliminating spool cap 154, pressure sensitive valveassembly 116 would be converted from a pressure sensitive valve assemblyto an acceleration sensitive valve assembly. In this configuration,motion of spool 152 would be defined by the mass of spool 152 and thedesign for valve spring 156. These specifications can be tuned to aspecific desired frequency and will provide a similar increase indamping force once closed. Final damping force will be defined byproviding bypass passage 166 as previously discussed.

Referring now to FIG. 6, base valve assembly 238 is illustrated. Basevalve assembly 238 comprises a piston 210, a rebound valve assembly 212,a compression valve assembly 214 and a pressure sensitive valve assembly216. Piston 210 is slidingly received in pressure tube 30 and separateslower working chamber 46 from reservoir chamber 52. Piston 210 defines acentral passage 224 extending between lower working chamber 46 andreservoir chamber 52, a plurality of rebound fluid passages 226extending between lower working chamber 46 and reservoir chamber 52 anda plurality of compression fluid passages 228 extending between lowerworking chamber 46 and reservoir chamber 52.

Rebound valve assembly 212 comprises one or more valve discs 230 and avalve spring 232 and a nut 234. Valve disc or valve discs 230 closes theplurality of rebound fluid passages 226 and valve spring 232 is disposedbetween nut 234 and valve disc 230 to bias valve disc 230 against piston210. Fluid access to compression fluid passages 228 is provided by aplurality of apertures which extend through valve disc 230. During arebound stroke of shock absorber 20, the “rod volume” concept requiresfluid to flow from reservoir chamber 52 to lower working chamber 46. Therebound stroke reduces the fluid pressure within lower working chamber46 and the fluid pressure within reservoir chamber 52 will exceed thefluid pressure within lower working chamber 46. The fluid pressurewithin reservoir chamber 52 will react against valve disc 230 and whenthe load on valve disc 230 from the fluid pressure exceeds the biasingload of valve spring 232, valve disc 230 will unseat from piston 210 andfluid will flow from reservoir chamber 52, through rebound fluidpassages 226 and into lower working chamber 46. Valve spring 232 isdesigned to exert a minimum load against valve disc 230 such thatrebound valve assembly 212 acts like a check valve during a reboundstroke and does not substantially contribute to the damping loads forshock absorber 20. The damping load during a rebound stroke for shockabsorber 20 is created by rebound valve assembly 64 of piston assembly32.

Compression valve assembly 214 comprises one or more valve discs 240 anda bolt 242. Valve discs 240 close the plurality of compression fluidpassages 228 and bolt 242 threadingly engages nut 234 to secure valvedisc 240 against piston 210. During a compression stroke of shockabsorber 20, the “rod volume” concept requires fluid to flow from lowerworking chamber 46 to reservoir chamber 52. During the compressionstroke, fluid pressure in lower working chamber 46 increases and thisfluid pressure reacts against valve discs 240. As the fluid pressurewithin lower working chamber 46 increases, the fluid pressure reactsagainst valve discs 240 and eventually valve discs 240 will deflect toopen compression fluid passages 228. Fluid will flow from lower workingchamber 46, through fluid passages 228 and into reservoir chamber 52.The damping load during a compression stroke is created by compressionvalve assembly 214. As described above, compression valve assembly 62 ofpiston assembly 32 acts like a check valve and does not substantiallycontribute to the damping loads for shock absorber 20. Compression valveassembly 214 is a normally closed compression valve assembly which isopened by the pressure differential between lower working chamber 46 andreservoir chamber 52. The flow through compression valve assembly 214 isdirectly proportional to the pressure differential. The greater thepressure differential, the greater deflection of valve discs 140 and thegreater the flow through compression valve assembly 214.

Pressure sensitive valve assembly 216 comprises piston 210, a cylinderend 250 and a biasing spring 252. Cylinder end 250 is attached topressure tube 30 and it engages end cap 54. Piston 210 is slidablydisposed within pressure tube 30 and slides between cylinder end 250 anda stop 254. Biasing spring 252 urges piston 210 towards stop 254.Cylinder end 250 defines one or more apertures 256 which allow fluidflow between lower working chamber 46 and reservoir chamber 52.

During a compression stroke, fluid pressure within lower working chamber46 acts against the upper side of piston 210. The fluid pressure withinreservoir chamber 52 acts against the lower side of piston 210. Thebiasing load of biasing spring 252 allows for the normal flow of fluidthrough compression valve assembly 214 as described above as long as thepressure differential across piston 210 does not generate sufficientload to overcome the biasing load of biasing spring 252. Once thepressure differential across piston 210 generates sufficient load toovercome the biasing load of biasing spring 252, piston 210 will slidedownward in pressure tube 30. As piston 210 approaches cylinder end 250,compression valve assembly 214 will contact a land 258 on cylinder end250 and close or prohibit fluid flow from lower working chamber 46through apertures 256 to reservoir chamber 52. When the fluid pressuredifference across piston 210 reduces, biasing spring 252 will again biaspiston 210 against stop 254. As illustrated, valve discs 240 contactland 258 but the present invention is not limited to this concept asother components could prohibit fluid flow. Pressure sensitive valveassembly 216 is a normally open compression valve assembly which isclosed by the pressure differential between lower working chamber 46 andreservoir chamber 52 where the pressure differential is determined bythe velocity of piston assembly 32.

The fluid pressure in lower working chamber 46 exponentially increasesand the only flow between lower working chamber 46 and reservoir chamber52 is through a bypass 266 defined by compression valve assembly 214 orby compression valve assembly 214 and pressure sensitive valve assembly216. Bypass 266 can include a passage around or through valve discs 240or a bypass passage defined by piston 210 and cylinder end 250. The areaof bypass 266 and the instantaneous velocity of piston assembly 32 willdefine the final damping forces achieved. The increase in fluid pressurewithin lower working chamber 46 is function of the velocity of pistonassembly 32 and thus, pressure sensitive valve assembly 216 is apressure sensitive valve which opens and closes based upon the velocityof piston assembly 32.

Referring now to FIG. 7, base valve assembly 338 is illustrated. Basevalve assembly 338 comprises piston 210, rebound valve assembly 212,compression valve assembly 214 and a pressure sensitive valve assembly316. Piston 210 is slidingly received in pressure tube 30 and separateslower working chamber 46 from reservoir chamber 52. Piston 210 definescentral passage 224 extending between lower working chamber 46 andreservoir chamber 52, the plurality of rebound fluid passages 226extending between lower working chamber 46 and reservoir chamber 52 andthe plurality of compression fluid passages 228 extending between lowerworking chamber 46 and reservoir chamber 52.

Rebound valve assembly 212 comprises the one or more valve discs 230,valve spring 232 and nut 234. Valve disc or valve discs 230 close theplurality of rebound fluid passages 226 and valve spring 232 is disposedbetween nut 234 and valve disc 230 to bias valve disc 230 against piston210. Fluid access to compression fluid passages 228 is provided by aplurality of apertures which extend through valve disc 230. During arebound stroke of shock absorber 20, the “rod volume” concept requiresfluid to flow from reservoir chamber 52 to lower working chamber 46. Therebound stroke reduces the fluid pressure within lower working chamber46 and the fluid pressure within reservoir chamber 52 will exceed thefluid pressure within lower working chamber 46. The fluid pressurewithin reservoir chamber 52 will react against valve disc 230 and whenthe load on valve disc 230 from the fluid pressure exceeds the biasingload of valve spring 232, valve disc 230 will unseat from piston 210 andfluid will flow from reservoir chamber 52, through rebound fluidpassages 226 and into lower working chamber 46. Valve spring 232 isdesigned to exert a minimum load against valve disc 230 such thatrebound valve assembly 212 acts like a check valve during a reboundstroke and does not substantially contribute to the damping loads forshock absorber 20. The damping load during a rebound stroke for shockabsorber 20 is created by rebound valve assembly 64 of piston assembly32.

Compression valve assembly 214 comprises the one or more valve discs 240and bolt 242. Valve discs 240 close the plurality of compression fluidpassages 228 and bolt 242 threadingly engages nut 234 to secure valvedisc 240 against piston 210. During a compression stroke of shockabsorber 20, the “rod volume” concept requires fluid to flow from lowerworking chamber 46 to reservoir chamber 52. During the compressionstroke, fluid pressure in lower working chamber 46 increases and thisfluid pressure reacts against valve discs 240. As the fluid pressurewithin lower working chamber 46 increases, the fluid pressure reactsagainst valve discs 240 and eventually valve discs 240 will deflect toopen compression fluid passages 228. Fluid will flow from lower workingchamber 46, through fluid passages 228 and into reservoir chamber 52.The damping load during a compression stroke is created by compressionvalve assembly 214. As described above, compression valve assembly 62 ofpiston assembly 32 acts like a check valve and does not substantiallycontribute to the damping loads for shock absorber 20. Compression valveassembly 214 is a normally closed compression valve assembly which isopened by the pressure differential between lower working chamber 46 andreservoir chamber 52. The flow through compression valve assembly 214 isdirectly proportional to the pressure differential. The greater thepressure differential, the greater deflection of valve discs 140 and thegreater the flow through compression valve assembly 214.

Pressure sensitive valve assembly 316 comprises a cylinder end 350 and abiasing spring 352. Cylinder end 350 is attached to pressure tube 30 andit engages end cap 54. Piston 210 is slidably disposed within pressuretube 30 and slides between cylinder end 350 and a stop 354. Biasingspring 352 urges piston 210 towards a stop 354. Cylinder end 350 definesone or more apertures 356 which allow fluid flow between lower workingchamber 46 and reservoir chamber 52.

During a compression stroke, fluid pressure within lower working chamber46 acts against the upper side of piston 210. The fluid pressure withinreservoir chamber 52 acts against the lower side of piston 210. Thebiasing load of biasing spring 352 allows for the normal flow of fluidthrough compression valve assembly 214 as described above as long as thepressure differential across piston 210 does not generate sufficientload to overcome the biasing load of biasing spring 352. Once thepressure differential across piston 210 generates sufficient load toovercome the biasing load of biasing spring 352, piston 210 will slidedown in pressure tube 30. As piston 210 approaches cylinder end 350,biasing spring 352 will interface with a sealing land 358 on cylinderend 350 to close or prohibit fluid flow from lower working chamber 46 toreservoir chamber 52 through apertures 356. When the fluid pressuredifference across piston 210 reduces, biasing spring 352 will again biaspiston 210 against stop 354. As illustrated, biasing spring 352interfaces with cylinder end 350 but the present disclosure is notlimited to this concept as other components could prohibit the fluidflow. Pressure sensitive valve assembly 316 is a normally opencompression valve assembly which is closed by the pressure differentialbetween lower working chamber 46 and reservoir chamber 52 where thepressure differential is determined by the velocity of piston assembly32.

The fluid pressure in lower working chamber 46 exponentially increasesand the only flow between lower working chamber 46 and reservoir chamber52 is through a bypass 366 defined by compression valve assembly 214 orby compression valve assembly 214 and pressure sensitive valve assembly316. Bypass 366 can include a passage around or through cylinder end350. The area of bypass 366 and the instantaneous velocity of pistonassembly 32 will define the final damping forces achieved. The increasein fluid pressure within lower working chamber 46 is a function of thevelocity of piston assembly 32 and thus pressure sensitive valveassembly 316 is a pressure sensitive valve which opens and closes basedupon the velocity of piston assembly 32.

Referring now to FIG. 8, base valve assembly 438 is illustrated. Basevalve assembly 438 comprises piston 210, rebound valve assembly 212,compression valve assembly 214 and a pressure sensitive valve assembly416. Piston 210 is slidingly received in pressure tube 30 and separateslower working chamber 46 from reservoir chamber 52. Piston 210 definescentral passage 224 extending between lower working chamber 46 andreservoir chamber 52, the plurality of rebound fluid passages 226extending between lower working chamber 46 and reservoir chamber 52 andthe plurality of compression fluid passages 228 extending between lowerworking chamber 46 and reservoir chamber 52.

Rebound valve assembly 212 comprises the one or more valve discs 230valve spring 232 and nut 234. Valve discs 230 close the plurality ofrebound fluid passages 226 and valve spring 232 is disposed between nut234 and valve disc 230 to bias valve disc 230 against piston 210. Fluidaccess to compression fluid passages 228 is provided by a plurality ofapertures which extend through valve disc 230. During a rebound strokeof shock absorber 20, the “rod volume” concept requires fluid to flowfrom reservoir chamber 52 to lower working chamber 46. The reboundstroke reduces the fluid pressure within lower working chamber 46 andthe fluid pressure within reservoir chamber 52 will exceed the fluidpressure within lower working chamber 46. The fluid pressure withinreservoir chamber 52 will react against valve disc 230 and when the loadon valve disc 230 from the fluid pressure exceeds the biasing load ofvalve spring 232, valve disc 230 will unseat from piston 210 and fluidwill flow from reservoir chamber 52, through rebound fluid passages 226and into lower working chamber 46. Valve spring 232 is designed to exerta minimum load against valve disc 230 such that rebound valve assembly212 acts like a check valve during a rebound stroke and does notsubstantially contribute to the damping loads for shock absorber 20. Thedamping load during a rebound stroke for shock absorber 20 is created byrebound valve assembly 64 of piston assembly 32.

Compression valve assembly 214 comprises the one or more valve discs 240and bolt 242. Valve discs 240 close the plurality of compression fluidpassages 228 and bolt 242 threadingly engages nut 234 to secure valvedisc 240 against piston 210. During a compression stroke of shockabsorber 20, the “rod volume” concept requires fluid to flow from lowerworking chamber 46 to reservoir chamber 52. During the compressionstroke, fluid pressure in lower working chamber 46 increases and thisfluid pressure reacts against valve discs 240. As the fluid pressurewithin lower working chamber 46 increases, the fluid pressure reactsagainst valve discs 240 and eventually valve discs 240 will deflect toopen compression fluid passages 228. Fluid will flow from lower workingchamber 46, through fluid passages 228 and into reservoir chamber 52.The damping load during a compression stroke is created by compressionvalve assembly 214. As described above, compression valve assembly 62 ofpiston assembly 32 acts like a check valve and does not substantiallycontribute to the damping loads for shock absorber 20. Compression valveassembly 214 is a normally closed compression valve assembly which isopened by the pressure differential between lower working chamber 46 andreservoir chamber 52. The flow through compression valve assembly 214 isdirectly proportional to the pressure differential. The greater thepressure differential, the greater deflection of valve discs 240 and thegreater the flow through compression valve assembly 214.

Pressure sensitive valve assembly 416 comprises piston 210, a cylinderend 450 and a biasing spring 452. Cylinder end 450 is attached topressure tube 30 and it engages end cap 54. Piston 210 is slidablydisposed within pressure tube 30 and slides between cylinder end 450 anda stop 454. Biasing spring 452 urges piston 210 towards stop 454.Cylinder end 450 defines one or more apertures 456 which allow fluidflow between lower working chamber 46 and reservoir chamber 52.

During a compression stroke, fluid pressure within lower working chamber46 acts against the upper side of piston 210. The fluid pressure withinreservoir chamber 52 acts against the lower side of piston 210. Thebiasing load of biasing spring 452 allows for the normal flow of fluidthrough compression valve assembly 214 as described above as long as thepressure differential across piston 210 does not generate sufficientload to overcome the biasing load of biasing spring 452. Once thepressure differential across piston 210 generates sufficient load toovercome the biasing load of biasing spring 452, piston 210 will slidedownward in pressure tube 30. As piston 210 approaches cylinder end 450,bolt 242 will contact cylinder end 450 and close or prohibit fluid flowfrom lower working chamber 46 through apertures 456 to reservoir chamber52. When the fluid pressure difference across piston 210 reduces,biasing spring 452 will again bias piston 210 against stop 454. Asillustrated, bolt 242 contacts cylinder end 450 but the presentinvention is not limited to this concept as other components couldprohibit fluid flow. Pressure sensitive valve assembly 416 is a normallyopen compression valve assembly which is closed by the pressuredifferential between lower working chamber 46 and reservoir chamber 52where the pressure differential is determined by the velocity of pistonassembly 32.

The fluid pressure in lower working chamber 46 exponentially increasesand the only flow between lower working chamber 46 and reservoir chamber52 is through a bypass 466 defined by compression valve assembly 214 orby compression valve assembly 214 and pressure sensitive valve assembly216. Bypass 466 can include a passage around or through cylinder end450. The area of bypass 466 and the instantaneous velocity of pistonassembly 32 will define the final damping forces achieved. The increasein fluid pressure within lower working chamber 46 is function of thevelocity of piston assembly 32 and thus, pressure sensitive valveassembly 416 is a pressure sensitive valve which opens and closes basedupon the velocity of piston assembly 32.

Referring now to FIG. 9, base valve assembly 538 is illustrated. Basevalve assembly 538 comprises piston 210, rebound valve assembly 212,compression valve assembly 214 and a pressure sensitive valve assembly516. Piston 210 is attached to pressure tube 30 and separates lowerworking chamber 46 from reservoir chamber 52. Piston 210 defines centralpassage 224 extending between lower working chamber 46 and reservoirchamber 52, the plurality of rebound fluid passages 226 extendingbetween lower working chamber 46 and reservoir chamber 52 and theplurality of compression fluid passages 228 extending between lowerworking chamber 46 and reservoir chamber 52.

Rebound valve assembly 212 comprises the one or more valve discs 230,valve spring 232 and nut 234. Valve discs 230 close the plurality ofrebound fluid passages 226 and valve spring 232 is disposed between nut234 and valve disc 230 to bias valve disc 230 against piston 210. Fluidaccess to compression fluid passages 228 is provided by a plurality ofapertures which extend through valve disc 230. During a rebound strokeof shock absorber 20, the “rod volume” concept requires fluid to flowfrom reservoir chamber 52 to lower working chamber 46. The reboundstroke reduces the fluid pressure within lower working chamber 46 andthe fluid pressure within reservoir chamber 52 will exceed the fluidpressure within lower working chamber 46. The fluid pressure withinreservoir chamber 52 will react against valve disc 230 and when the loadon valve disc 230 from the fluid pressure exceeds the biasing load ofvalve spring 232, valve disc 230 will unseat from piston 210 and fluidwill flow from reservoir chamber 52, through rebound fluid passages 226and into lower working chamber 46. Valve spring 232 is designed to exerta minimum load against valve disc 230 such that rebound valve assembly212 acts like a check valve during a rebound stroke and does notsubstantially contribute to the damping loads for shock absorber 20. Thedamping load during a rebound stroke for shock absorber 20 is created byrebound valve assembly 64 of piston assembly 32.

Compression valve assembly 214 comprises the one or more valve discs 240and bolt 242. Valve discs 240 close the plurality of compression fluidpassages 228 and bolt 242 threadingly engages nut 234 to secure valvedisc 240 against cylinder end 250. During a compression stroke of shockabsorber 20, the “rod volume” concept requires fluid to flow from lowerworking chamber 46 to reservoir chamber 52. During the compressionstroke, fluid pressure in lower working chamber 46 increases and thisfluid pressure reacts against valve discs 240. As the fluid pressurewithin lower working chamber 46 increases, the fluid pressure reactsagainst valve discs 240 and eventually valve discs 240 will deflect toopen compression fluid passages 228. Fluid will flow from lower workingchamber 46, through fluid passages 228 and into reservoir chamber 52.The damping load during a compression stroke is created by compressionvalve assembly 214. As described above, compression valve assembly 62 ofpiston assembly 32 acts like a check valve and does not substantiallycontribute to the damping loads for shock absorber 20. Compression valveassembly 214 is a normally closed compression valve assembly which isopened by the pressure differential between lower working chamber 46 andreservoir chamber 52. The flow through compression valve assembly 214 isdirectly proportional to the pressure differential. The greater thepressure differential, the greater deflection of valve discs 140 and thegreater the flow through compression valve assembly 214.

Pressure sensitive valve assembly 516 comprises piston 210, a cylinderend 550 and a biasing spring 552. Cylinder end 550 is attached topressure tube 30 and it engages end cap 54. Piston 210 is slidablydisposed within pressure tube 30 and slides between cylinder end 550 anda stop 554. Biasing spring 552 urges piston 210 towards stop 554.Pressure tube 30 defines one or more apertures 556 which allow fluidflow between lower working chamber 46 and reservoir chamber 52.

During a compression stroke, fluid pressure within lower working chamber46 acts against the upper side of piston 210. The fluid pressure withinreservoir chamber 52 acts against the lower side of piston 210. Thebiasing load of biasing spring 552 allows for the normal flow of fluidthrough compression valve assembly 214 as described above as long as thepressure differential across piston 210 does not generate sufficientload to overcome the biasing load of biasing spring 552. Once thepressure differential across piston 210 generates sufficient load toovercome the biasing load of biasing spring 552, piston 210 will slidedownward in pressure tube 30. As piston 210 approaches cylinder end 550,piston 210 will begin to cover apertures 556 and close or prohibit fluidflow from lower working chamber 46 through apertures 556 to reservoirchamber 52. When the fluid pressure difference across piston 210reduces, biasing spring 552 will again bias piston 210 against stop 554.Pressure sensitive valve assembly 516 is a normally open compressionvalve assembly which is closed by the pressure differential betweenlower working chamber 46 and reservoir chamber 52 where the pressuredifferential is determined by the velocity of piston assembly 32.

The fluid pressure in lower working chamber 46 exponentially increasesand the only flow between lower working chamber 46 and reservoir chamber52 is through a bypass 566 defined by compression valve assembly 214 orby compression valve assembly 214 and pressure sensitive valve assembly216. Bypass 566 can include a bypass passage defined by piston 210 andpressure tube 30. The area of bypass 566 and the instantaneous velocityof piston assembly 32 will define the final damping forces achieved. Theincrease in fluid pressure within lower working chamber 46 is functionof the velocity of piston assembly 32 and thus, pressure sensitive valveassembly 516 is a pressure sensitive valve which opens and closes basedupon the velocity of piston assembly 32.

Referring now to FIG. 10, base valve assembly 638 is illustrated. Basevalve assembly 638 comprises piston 210, rebound valve assembly 212,compression valve assembly 214 and pressure sensitive valve assembly616. Piston 210 is attached to pressure tube 30 and separates lowerworking chamber 46 from reservoir chamber 52. Piston 210 defines acentral passage 224 extending between lower working chamber 46 andreservoir chamber 52, the plurality of rebound fluid passages 226extending between lower working chamber 46 and reservoir chamber 52 andthe plurality of compression fluid passages 228 extending between lowerworking chamber 46 and reservoir chamber 52.

Rebound valve assembly 212 comprises the one or more valve discs 230,valve spring 232 and nut 234. Valve discs 230 close the plurality ofrebound fluid passages 226 and valve spring 232 is disposed between nut234 and valve disc 230 to bias valve disc 230 against piston 210. Fluidaccess to compression fluid passages 228 is provided by a plurality ofapertures which extend through valve disc 230. During a rebound strokeof shock absorber 20, the “rod volume” concept requires fluid to flowfrom reservoir chamber 52 to lower working chamber 46. The reboundstroke reduces the fluid pressure within lower working chamber 46 andthe fluid pressure within reservoir chamber 52 will exceed the fluidpressure within lower working chamber 46. The fluid pressure withinreservoir chamber 52 will react against valve disc 230 and when the loadon valve disc 230 from the fluid pressure exceeds the biasing load ofvalve spring 232, valve disc 230 will unseat from piston 210 and fluidwill flow from reservoir chamber 52 through rebound fluid passages 226and into lower working chamber 46. Valve spring 232 is designed to exerta minimum load against valve disc 230 such that rebound valve assembly212 acts like a check valve during a rebound stroke and does notsubstantially contribute to the damping loads for shock absorber 20. Thedamping load during a rebound stroke for shock absorber 20 is created byrebound valve assembly 64 of piston assembly 32.

Compression valve assembly 214 comprises the one or more valve discs 240and bolt 242. Valve discs 240 close the plurality of compression fluidpassages 228 and bolt 242 threadingly engages nut 234 to secure valvedisc 240 against piston 210. During a compression stroke of shockabsorber 20, the “rod volume” concept requires fluid to flow from lowerworking chamber 46 to reservoir chamber 52. During the compressionstroke, fluid pressure in lower working chamber 46 increases and thisfluid pressure reacts against valve discs 240. As the fluid pressurewithin lower working chamber 46 increases, the fluid pressure reactsagainst valve discs 240 and eventually valve discs 240 will deflect toopen compression fluid passages 228. Fluid will flow from lower workingchamber 46, through fluid passages 228 and into reservoir chamber 52.The damping load during a compression stroke is created by compressionvalve assembly 214. As described above, compression valve assembly 62 ofpiston assembly 32 acts like a check valve and does not substantiallycontribute to the damping loads for shock absorber 20. Compression valveassembly 214 is a normally closed compression valve assembly which isopened by the pressure differential between lower working chamber 46 andreservoir chamber 52. The flow through compression valve assembly 214 isdirectly proportional to the pressure differential. The greater thepressure differential, the greater deflection of valve discs 140 and thegreater the flow through compression valve assembly 214.

Pressure sensitive valve assembly 616 comprises a pressure tube cylinderend 650, a valve tube 652, a cylinder end 654, a piston and sleeveassembly 656 and a biasing spring 658 which is illustrated as aBelleville spring. Pressure tube cylinder end 650 is attached topressure tube 30 and to valve tube 652. Cylinder end 654 is attached tovalve tube 652 and engages end cap 54. Piston 210 is attached to pistonand sleeve assembly 656 and piston and sleeve assembly 656 is slidablydisposed within valve tube 652. A spacer 660 is disposed between pistonand sleeve assembly 656 and biasing spring 658. A seal 662 seals theinterface between piston and sleeve assembly 656 and valve tube 652.Biasing spring 658 urges piston and sleeve assembly 656 towards pressuretube cylinder end 650. Cylinder end 654 defines one or more apertures664 which allow fluid flow between lower working chamber 46 andreservoir chamber 52.

During a compression stroke, fluid pressure within lower working chamber46 acts against the upper side of piston 210. The fluid pressure withinreservoir chamber 52 acts against the lower side of piston 210. Thebiasing load of biasing spring 658 allows for the normal flow of fluidthrough compression valve assembly 214 as described above as long as thepressure differential across piston 210 does not generate sufficientload to overcome the biasing load of biasing spring 658. Once thepressure differential across piston 210 generates sufficient load toovercome the biasing load of biasing spring 658, piston 210 will causepiston and sleeve assembly 656 to slide down in valve tube 652. Aspiston and sleeve assembly 656 approaches cylinder end 654, biasingspring 658 will interface with cylinder end 654 to close or prohibitfluid flow from lower working chamber 46 to reservoir chamber 52 throughapertures 664. When the fluid pressure difference across piston 210reduces, biasing spring 658 will again bias piston and sleeve assembly656 against pressure tube cylinder end 650. As illustrated, biasingspring 658 interfaces with cylinder end 654 but the present disclosureis not limited to this concept as other components could prohibit thefluid flow. Pressure sensitive valve assembly 616 is a normally opencompression valve assembly which is closed by the pressure differentialbetween lower working chamber 46 and reservoir chamber 52 where thepressure differential is determined by the velocity of piston assembly32.

The fluid pressure in lower working chamber 46 exponentially increasesand the only flow between lower working chamber 46 and reservoir chamber52 is through a bypass 666 defined by compression valve assembly 214 andcylinder end 654 or by compression valve assembly 214 and pressuresensitive valve assembly 616. Bypass 666 can include a passage around orthrough cylinder end 654. The area of bypass 666 and the instantaneousvelocity of piston assembly 32 will define the final damping forcesachieved. The increase in fluid pressure within lower working chamber 46is a function of the velocity of piston assembly 32 and thus pressuresensitive valve assembly 616 is a pressure sensitive valve which opensand closes based upon the velocity of piston assembly 32.

Referring now to FIG. 11, a monotube shock absorber 720 is illustrated.Shock absorber 720 comprises a pressure tube 730, a piston assembly 732,a piston rod 734, an accumulator piston 736 and a pressure sensitivevalve assembly 738.

Pressure tube 730 defines a working chamber 742. Piston assembly 732 isslidably disposed within pressure tube 730 and divides pressure tube 730into an upper working chamber 744 and a lower working chamber 746. Aseal is disposed between piston assembly 732 and pressure tube 730 topermit sliding movement of piston assembly 732 with respect to pressuretube 730 without generating undue frictional forces as well as sealingupper working chamber 744 from lower working chamber 746. Piston rod 734is attached to piston assembly 732 and extends through upper workingchamber 744 and through an upper end cap or rod guide 750 which closesthe upper end of pressure tube 730. A sealing system seals the interfacebetween rod guide 750, pressure tube 730 and piston rod 734. The end ofpiston rod 734 opposite to piston assembly 732 is adapted to be securedto the sprung or unsprung portion of vehicle 10. The end of pressuretube 730 opposite to rod guide 750 is adapted to be connected to theother sprung or unsprung portion of vehicle 10.

An rebound valve assembly 760 controls the movement of fluid betweenupper working chamber 744 and lower working chamber 746 to generate thedamping forces during an extension movement of piston assembly 732 inpressure tube 730 as is well known in the art. A compression valveassembly 762 controls the movement of fluid between lower workingchamber 746 and upper working chamber 744 to generate the damping forcesduring a compression movement of piston assembly 732 in pressure tube730 as is well known in the art. Accumulator piston 736 separates lowerworking chamber 746 from an accumulator chamber 764 typically filledwith a gas. Accumulator piston 736 is slidably disposed within pressuretube 730 and with accumulator chamber 764, accumulator piston 736compensates for the “rod volume” concept as is well known in the art.

Pressure sensitive valve assembly 738 is a pressure actuated valveassembly which comprises a cylinder end 766, stem 150, spool 152, spoolcap 154, valve spring 156 and a bolt 768. The cylinder end 766 may befixedly secured to the pressure tube 730. Stem 150 is disposed within acentral passage 770 extending through cylinder end 766. Stem 150 issecured to cylinder end 766 by bolt 768. Bolt 768 defines a centralfluid passage 772 which is in communication with fluid passage 160 instem 150 to provide a bypass flow of fluid as described below.

Spool 152 is slidingly received over stem 150. Upward movement of spool152 on stem 150 is limited by flange 162 on stem 150 which engagesshoulder 164 defined by spool 152. Valve spring 156 biases shoulder 164of spool 152 against flange 162 of stem 150 to allow fluid to flow fromlower working chamber 46 into a plurality of fluid passages 776extending through cylinder end 766. Spool cap 154 is secured to spool152. Spool 152 defines the one or more holes 166.

During a compression stroke, fluid pressure within lower working chamber46 acts against spool 152 and spool cap 154 of pressure sensitive valveassembly 738. The fluid pressure below cylinder end 766 acts againstspool 152 and spool cap 154 of pressure sensitive valve assembly 738.The fluid pressure is channeled to spool 152 and spool cap 154 throughbypass passage 778. The biasing of valve spring 156 allows for thenormal flow of fluid through the plurality of fluid passages 776 toallow for the normal damping of shock absorber 720 since the fluid flowseasily to the area between pressure sensitive valve assembly 738 andaccumulator piston 736. Once the pressure differential acting on spool152 exceeds the biasing load of valve spring 156, spool 152 will slidedownward on stem 150 and close or prohibit fluid flow from lower workingchamber 46 through the plurality of passages 776. Once the fluidpressure across spool 152 reduces, valve spring 156 will again biasspool 152 upward against flange 162. When spool 152 closes or prohibitsfluid flow, the fluid pressure in lower working chamber 46 exponentiallyincreases and the only flow between lower working chamber 46 and thearea below cylinder end 766 is through the one or more holes 166. Thearea of the one or more holes 166 and the instantaneous velocity ofpiston assembly 732 will define the final damping forces achieved. Theincrease in fluid pressure within lower working chamber 746 is afunction of the velocity of piston assembly 732 and thus pressuresensitive valve assembly 738 is a pressure sensitive valve which opensand closes based upon the velocity of piston assembly 732. Pressuresensitive valve assembly 738 is a normally open compression valveassembly which is closed by the pressure differential between lowerworking chamber 746 and the area below cylinder end 766 where thepressure differential is determined by the velocity of piston assembly732.

Referring now to FIGS. 12 and 13, base valve assembly 838 isillustrated. Base valve assembly 838 comprises cylinder end 110, reboundvalve assembly 112, compression valve assembly 114 and a pressuresensitive valve assembly 816. Cylinder end 110 is attached to pressuretube 30 and separates lower working chamber 46 from reservoir chamber52. Cylinder end 110 engages end cap 54 and it defines a plurality offluid passages 122 open to reservoir chamber 52. Cylinder end 110defines the central passage 124 extending between lower working chamber46 and reservoir chamber 52 through fluid passages 122, the plurality ofrebound fluid passages 126 extending between lower working chamber 46and reservoir chamber 52 through fluid passages 122 and the plurality ofcompression fluid passages 128 extending between lower working chamber46 and reservoir chamber 52 through fluid passages 122.

Rebound valve assembly 112 comprises one or more valve discs 130 andvalve spring 132. Valve discs 130 close the plurality of rebound fluidpassages 126 and valve spring 132 is disposed between pressure sensitivevalve assembly 816 and valve disc 130 to bias valve disc 130 againstcylinder end 110. During a rebound stroke of shock absorber 20, the “rodvolume” concept requires fluid to flow from reservoir chamber 52 tolower working chamber 46. The rebound stroke reduces the fluid pressurewithin lower working chamber 46 and the fluid pressure within reservoirchamber 52 will exceed the fluid pressure within lower working chamber46. The fluid pressure within reservoir chamber 52 will react againstvalve disc 130 and when the load on valve disc 130 from the fluidpressure exceeds the biasing load of valve spring 132, valve disc 130will unseat from cylinder end 110 and fluid will flow from reservoirchamber 52 through fluid passages 122, through rebound fluid passages126 and into lower working chamber 46. Valve spring 132 is designed toexert a minimum load against valve disc 130 such that rebound valveassembly 112 acts like a check valve during a rebound stroke and doesnot substantially contribute to the damping loads for shock absorber 20.The damping load during a rebound stroke for shock absorber 20 iscreated by rebound valve assembly 64 of piston assembly 32.

Compression valve assembly 114 comprises one or more valve discs 140 anda bolt 142. Valve discs 140 close the plurality of compression fluidpassages 128 and bolt 142 threadingly engages pressure sensitive valveassembly 116 to secure valve disc 140 against cylinder end 110. During acompression stroke of shock absorber 20, the “rod volume” conceptrequires fluid to flow from lower working chamber 46 to reservoirchamber 52. During the compression stroke, fluid pressure in lowerworking chamber 46 increases and this fluid pressure reacts againstvalve discs 140. As the fluid pressure within lower working chamber 46increases, the fluid pressure reacts against valve discs 140 andeventually valve discs 140 will deflect to open compression fluidpassages 128. Fluid will flow from lower working chamber 46, throughcompression fluid passages 128, through fluid passages 122 and intoreservoir chamber 52. The damping load during a compression stroke iscreated by compression valve assembly 114. As described above,compression valve assembly 62 of piston assembly 32 acts like a checkvalve and does not substantially contribute to the damping loads forshock absorber 20. Compression valve assembly 114 is a normally closedcompression valve assembly which is opened by the pressure differentialbetween lower working chamber 46 and reservoir chamber 52. The flowthrough compression valve assembly 114 is directly proportional to thepressure differential. The greater the pressure differential, thegreater deflection of valve discs 140 and the greater the flow throughcompression valve assembly 114.

Pressure sensitive valve assembly 816 is a pressure actuated valveassembly which comprises cylinder end 110, stem 150, spool 152, spoolcap 154, a valve spring 856 and a valve disc 858. Valve spring 856 andvalve disc 858 define a secondary valve assembly 860. Stem 150 isdisposed within central passage 124 and is secured to cylinder end 110by bolt 142 of compression valve assembly 114. Bolt 142 defines centralfluid passage 158 and stem 150 defines central fluid passage 160 toprovide for a pressure drop as described below.

Spool 152 is slidingly received over stem 150. Upward movement of spool152 on stem 150 is limited by flange 162 on stem 150 which engagesshoulder 164 defined by spool 152. Valve spring 132 of rebound valveassembly 112 and valve spring 856 of pressure sensitive valve assembly116 biases shoulder 164 of spool 152 against flange 162 of stem 150 toallow fluid to flow from lower working chamber 46 into the plurality ofcompression fluid passages 128. Spool cap 154 is secured to spool 152.Spool 152 defines one or more holes 166. Valve disc 858 is biasedagainst spool 152 to close the one or more holes 166.

During a compression stroke, fluid pressure within lower working chamber46 acts against spool 152 and spool cap 154 of pressure sensitive valveassembly 816. The fluid pressure within reservoir chamber 52 actsagainst spool 152 and spool cap 154 of pressure sensitive valve assembly816. The reservoir fluid pressure is channeled to spool 152 and spoolcap 154 through fluid passages 122, 158 and 160. The biasing of valvespring 132 and valve spring 856 allows for the normal flow of fluidthrough compression valve assembly 114 as described above as long as thepressure difference across spool 152 does not generate sufficient loadto overcome the biasing load of valve spring 132 and valve spring 856.Once the pressure differential between fluid in lower working chamber 46and reserve chamber 52 acting against surfaces on spool 152 and spoolcap 154 exceeds the biasing load of valve spring 132 and valve spring856, spool 152 will slide downward on stem 150 and close or prohibitfluid flow from lower working chamber 46 to the plurality of compressionfluid passages 128 as illustrated in FIG. 13. Once the fluid pressureacross spool 152 reduces, valve spring 132 and valve spring 856 willagain bias spool 152 upward against flange 162. When spool 152 closes orprohibits fluid flow, the fluid pressure in lower working chamber 46exponentially increases and the only flow between lower working chamber46 and reservoir chamber 58 is through the one or more holes 166 andcompression valve assembly 114. As discussed above, the one or moreholes 166 are closed by valve disc 858 which is biased against spool 152by valve spring 856. When spool 152 closes, before fluid flow can flowthrough the one or more holes 166, the fluid pressure in lower workingchamber 46 must overcome the biasing of valve spring 856. The size ofthe one or more holes 166 will determine the pressure area open to valvedisc 858 setting the opening point for valve disc 858. If necessary, anadditional port (not shown) can be added on the circumference of spool152 for force characteristic tuning. The combined/total area of the oneor more holes 166 plus any additional ports and the instantaneousvelocity of piston assembly 32 will define the final damping forcesachieved. The increase in fluid pressure within lower working chamber 46is a function of the velocity of piston assembly 32 and thus pressuresensitive valve assembly 816 is a pressure sensitive valve which opensand closes based upon the velocity of piston assembly 32. Pressuresensitive valve assembly 816 is a normally open compression valveassembly which is closed by the pressure differential between lowerworking chamber 46 and reservoir chamber 52 where the pressuredifferential is determined by the velocity of piston assembly 32.

The movement of spool 152 can be controlled or damped by controlling thediameter of central fluid passage 158 of bolt 142. As illustrated inFIG. 12, fluid chamber 170 is located above bolt 142. This volume mustbe displaced through central fluid passage 158 in order for spool 152 tomove downward. By controlling the diameter of central fluid passage 158the period of time that it takes spool 152 to move downward can becontrolled. Thus, a damping effect can be achieved in regard to thismotion of spool 152.

Pressure sensitive valve assembly 816 can also be converted to anacceleration sensitive valve assembly. By eliminating central fluidpassage 158 and eliminating spool cap 154, pressure sensitive valveassembly 816 would be converted from a pressure sensitive valve assemblyto an acceleration sensitive valve assembly. In this configuration,motion of spool 152 would be defined by the mass of spool 152 and thedesign for valve spring 132 and valve spring 856. These specificationscan be tuned to a specific desired frequency and will provide a similarincrease in damping force once closed. Final damping force will bedefined by providing bypass passage 166 as previously discussed.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the invention. Individual elements or features ofa particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the invention, and all such modificationsare intended to be included within the scope of the invention.

What is claimed is:
 1. A shock absorber comprising: a pressure tubeforming a working chamber; a piston body slidably disposed within saidworking chamber, said piston body dividing said working chamber into anupper working chamber and a lower working chamber; means for defining afluid chamber in communication with one of said upper working chamberand said lower working chamber; a compression valve assembly controllingfluid flow from said lower working chamber to said fluid chamber; apressure sensitive valve assembly separate from said compression valveassembly disposed between said lower working chamber and said fluidchamber, said pressure sensitive valve assembly movable from an openposition allowing fluid flow to said compression valve assembly fromsaid lower working chamber to a closed position restricting but noteliminating said fluid flow to said compression valve assembly from saidlower working chamber based upon a velocity of said piston body slidingin said pressure tube; and a secondary valve assembly separate from saidpressure sensitive valve assembly and said compression valve assemblyprohibiting all of said fluid flow to said compression valve assemblyfrom said lower working chamber when said pressure sensitive valveassembly is in said closed position and when said secondary valveassembly is in a closed position.
 2. The shock absorber according toclaim 1, wherein said defining means comprises a reserve tubesurrounding said pressure tube to form said fluid chamber between saidreserve tube and said pressure tube.
 3. The shock absorber according toclaim 1, wherein said defining means comprises a piston assemblyslidably disposed in said pressure tube, said fluid chamber beingdefined by said pressure tube.
 4. The shock absorber according to claim1, wherein said pressure sensitive valve assembly comprises a cylinderend attached to said pressure tube, a spool movable between an openposition and a closed position and a first biasing member urging saidspool into said open position.
 5. The shock absorber according to claim4, wherein said secondary valve assembly includes a valve disc and asecond biasing member urging said valve disc against said spool.
 6. Theshock absorber according to claim 5, wherein the second biasing memberurges said spool into said open position.
 7. The shock absorberaccording to claim 6, wherein the spool defines one or more holes, thevalve disc being urged against said spool to close said one or moreholes.
 8. The shock absorber according to claim 5, wherein the spooldefines one or more holes, the valve disc being urged against said spoolto close said one or more holes.
 9. The shock absorber according toclaim 1, wherein an increase of pressure of working fluid in said lowerworking chamber moves said pressure sensitive valve assembly from saidopen position to said closed position.
 10. The shock absorber accordingto claim 1, wherein said pressure sensitive valve assembly defines afirst surface in direct contact with working fluid in said lower workingchamber and a second surface in direct contact with working fluid insaid fluid chamber.
 11. The shock absorber according to claim 1, whereina difference in fluid pressure acting on said first and second surfacesmoves said pressure sensitive valve assembly between said open andclosed positions.
 12. A shock absorber comprising: a pressure tubeforming a first fluid chamber; a working fluid disposed within saidfirst fluid chamber; a piston body slidably disposed within said firstfluid chamber, said piston body dividing said first fluid chamber intoan upper working chamber and a lower working chamber; a second fluidchamber in communication with said lower working chamber; a first fluidvalve assembly disposed between said lower working chamber and saidsecond fluid chamber, said first fluid valve assembly allowing directfluid flow from said second fluid chamber to said lower working chamberwhile prohibiting fluid flow from said lower working chamber directly tosaid second fluid chamber; a second fluid valve assembly disposedbetween said lower working chamber and said second fluid chamber, saidsecond fluid valve assembly prohibiting fluid flow from said secondfluid chamber to said lower working chamber while allowing fluid flowfrom said lower working chamber to said second fluid chamber; a pressuresensitive valve assembly including a movable member spaced from thefirst and second fluid valve assemblies, said movable member of saidpressure sensitive valve assembly including at least one hole extendingtherethrough, and said pressure sensitive valve assembly being disposedbetween said lower working chamber and said second fluid chamber, andwherein: said pressure sensitive valve assembly operates independentlyfrom a position of said piston body within said first fluid chamber; afirst surface on said movable member of said pressure sensitive valveassembly always being in direct fluid contact with working fluiddisposed within said second fluid chamber such that fluid pressure insaid second fluid chamber acts directly on said first surface of saidpressure sensitive valve assembly; a second surface of said movablemember of said pressure sensitive valve assembly being in direct fluidcontact with working fluid disposed within said lower working chamber;movement of said movable member of said pressure sensitive valveassembly causing said pressure sensitive valve assembly to change froman open position to a closed position, said pressure sensitive valveassembly then restricting fluid flow through said second fluid valveassembly when said pressure sensitive valve assembly is in said closedposition such that fluid flow from said lower working chamber to saidsecond fluid chamber is limited by an area of said hole in said movablemember; said pressure sensitive valve assembly being operable to movebetween said open and closed positions to control fluid flow throughsaid second fluid valve assembly based upon a pressure differentialbetween pressure of said working fluid in said second fluid chamberreacting against said second surface of said movable member and pressureof said working fluid in said lower working chamber reacting againstsaid first surface of said movable member; the shock absorber furthercomprising: a secondary valve assembly controlling fluid flow throughsaid pressure sensitive valve assembly when said pressure sensitivevalve assembly is in said closed position.
 13. The shock absorberaccording to claim 12, wherein said second fluid chamber comprises areserve tube surrounding said pressure tube.
 14. The shock absorberaccording to claim 12, wherein said second fluid chamber is defined bysaid pressure tube, and wherein a piston assembly is slidably disposedin said pressure tube.
 15. The shock absorber according to claim 12,wherein said pressure sensitive valve assembly comprises a cylinder endattached to said pressure tube, a spool slidably disposed on saidcylinder end, said spool movable between an open position and a closedposition and a biasing member urging said spool into said open position,said pressure of said working fluid in said one of said upper workingchamber and said lower working chamber urging said spool into saidclosed position.
 16. The shock absorber according to claim 12, whereinsaid pressure sensitive valve assembly is fixedly secured to saidpressure tube.
 17. The shock absorber according to claim 12, whereinsaid pressure sensitive valve assembly defines a fluid passage extendingthrough said first and second fluid valve assemblies.
 18. The shockabsorber according to claim 12, wherein said pressure sensitive valveassembly comprises a stem, a spool, a spool cap and a spring, said spoolcap being said movable member.
 19. The shock absorber according to claim12, wherein said movable member is not a component of the first fluidvalve assembly.
 20. A shock absorber comprising: a pressure tube forminga first fluid chamber; a working fluid disposed within said first fluidchamber; a piston body slidably disposed within said first fluidchamber, said piston body dividing said first fluid chamber into anupper working chamber and a lower working chamber; means for defining asecond fluid chamber in communication with said lower working chamber; afirst fluid valve assembly disposed between said lower working chamberand said second fluid chamber, said first fluid valve assembly allowingdirect fluid flow from said second fluid chamber to said lower workingchamber while prohibiting fluid flow from said lower working chamberdirectly to said second fluid chamber; a second fluid valve assemblydisposed between said lower working chamber and said second fluidchamber, said second fluid valve assembly prohibiting fluid flow fromsaid second fluid chamber to said lower working chamber while allowingfluid flow from said lower working chamber to said second fluid chamber;a pressure sensitive valve assembly different from the first and secondfluid valve assemblies disposed between said lower working chamber andsaid second fluid chamber, said pressure sensitive valve assemblyincluding a movable member having a hole forming a fluid passagetherethrough; wherein said pressure sensitive valve operatesindependently from a position of said piston body within said firstfluid chamber; a first surface of said pressure sensitive valve assemblyalways being in direct contact with working fluid disposed within saidsecond fluid chamber; a second surface of said pressure sensitive valveassembly being in direct contact with working fluid disposed within saidlower working chamber; said pressure sensitive valve assembly is movablefrom an open position to a closed position based only upon a pressuredifferential between pressure of said working fluid in said second fluidchamber and pressure of said working fluid in said lower workingchamber, said pressure sensitive valve assembly using said hole to limitfluid flow through said second fluid valve assembly when said pressuresensitive valve assembly is in said closed position; the shock absorberfurther comprising: a secondary valve assembly controlling fluid flowthrough said pressure sensitive valve assembly when said pressuresensitive valve assembly is in said closed position.